An aerial vehicle can use an air turbine starter to start an engine. A starter air valve can be used to provide fluid to the air turbine starter. The air turbine starter can include an air turbine motor, a speed reducer, and an over-running clutch. The air turbine motor converts energy from the fluid supplied by the starter air valve to high speed rotation energy. The speed reducer converts the high speed, low torque input to low speed, high torque output usable by the engine. The over-running clutch allows for the de-coupling of the air turbine motor and speed reducer from the engine during normal engine operation.